1. Field of the Invention
The present invention relates to connector pin systems, and more particularly to a method and apparatus for hot swap of modules using connector pin systems.
2. Description of the Related Art
Electric systems used in complex environments such as aerospace systems, more electric aircraft systems, industrial environments, vehicles, etc., include a large number of electric modules. Various electric modules may need to be extracted and replaced with other electric modules, to change functionality or to replace electric modules that exhibit faults.
Hot swap, hot-plug, and hot-dock are terms used interchangeably to refer to the process of safely inserting or removing cards, PC boards, cables, and/or modules from a host system without removing power. The goal of hot swap is to insert or remove modules without disturbing, damaging, or degrading up/down-stream adjacent line replaceable modules/subsystems, to increase system availability, reduce down time, simplify system repair, and allow for system maintenance/upgrade without interrupting service to other loads.
If not designed for properly, hot swap can cause severe electrical, mechanical, thermal and operational problems in an electrical system. For example, random pin arcing may occur during the mating process of a replaceable module with its parent electrical system. Pulling a board/module out while there is current passing through the module connectors, or inserting a board/module with all bulk/bypass capacitors at zero volts, can introduce severe electrical voltage/current transients which may adversely impact reliability and lead to safety consequences. For example, current chopping introduces Ldi/dt variations (where L is inductance of a load, for example) leading to very large voltage transients which are a major safety concern for maintenance people, as large voltage transients can cause high voltage electrical shock.
Multiple long/short pin arrangements are used in typical/conventional hot swap of replaceable modules. One such pin arrangement is described in “Introduction to Hot Swap”, by Jonathan M. Bearfield, Texas Instruments, TechOnLine, publication date Sep. 24, 2001. In this publication, a hot swap system for hot swap of modules includes a connector with long and short pins, a fuse, and an RC circuit. During hot swap of a module, the long pins mate first, adding the RC circuit to pre-charge the module/board. When the board/module is fully inserted, the short pins mate, bypassing the resistor connected to the longer pins and creating a low impedance connection. One problem associated with long/short pin arrangements is the increase in number of pins needed for hot swap. Presence of more pins for hot swap leads to increased cost and weight of systems using such hot swap pin arrangements. A second problem associated with long/short pin arrangements for hot swap is lack of control in the timing of pin insertion and extraction during hot swap.
Some techniques to integrate long and short pins have been studied. One such technique is described in U.S. Pat. No. 4,747,783 titled “Resistive Pin for Printed Circuit Card Connector”, by P. D. Bellamy et al. In the technique described in this patent, a male connector pin is made of a conductive material, an outer layer of resistive material, and a layer of insulating material. The outer layer of resistive material is deposited on a first portion of the conductive material. The insulating layer separates the resistive layer from the conductive material. As the pin is inserted into an electrical socket, socket contacts travel first along the resistive portion of the pin, and then along the conductive portion of the pin. In this technique, however, the length of the socket-contacted resistive region of the pin increases to a maximum, before the socket contacts reach the conductive region of the pin. Hence, the resistance of the connector pin increases to a maximum, after which abruptly drops to zero, which leads to a non-uniform and not well controlled hot swap process. Moreover, a pin system as described in the above mentioned patent is difficult to manufacture and is not cost-effective, due to the configuration of layers on the pin connector.
A disclosed embodiment of the application addresses these and other issues by utilizing an integrated hot swap connector pin system that includes a conductive male pin, and a female pin with a resistive region, an insulating region, and a conductive region. The method and apparatus produce a gradually decreasing resistance as the male pin is inserted into the female pin, hence eliminating in-rush currents during hot swap insertion of a replaceable module into a live power board. The method and apparatus produce a gradually increasing resistance as the male pin is extracted from the female pin, hence reducing current chopping during hot swap extraction of a replaceable module from a live power board. The method and apparatus prevent random pin arcing during mating process by reducing the AC or DC current during the MAKE or BREAK process; eliminate in-rush currents during initial insertion of a board/module with all bulk/bypass capacitors at zero volts; eliminate large electrical voltage/current transients, such as large voltage transients due to Ldi/dt current chopping variations, which may adversely impact reliability and lead to safety consequences; provide a uniform and well controlled hot swap of replaceable modules and boards.